P - 106 Detection of sub-trappean sediments by Deep Resistivity Sounding studies in India S. B. Singh*, G. Ashok Babu, B.Veeraiah, V. Chakravarthi National Geophysical Research Institute, Hyderabad-500 007, India Summary Two hundred twenty Deep Resistivity Soundings (DRS) were conducted to detect the thickness of trap, sediments and basement topography in trap covered areas of Saurashtra, Kutch and Deccan Syneclise areas by using high power deep resistivity equipment. Mostly, Schlumberger, electrode configuration was deployed up to current electrode spacing of 10 km at each station and incase of necessity it was extended with equatorial dipole array up to 15 km spread. Applicability of DRS technique for exploration of subtrappean sediments is enhanced because sharp resistivity contrast exists between trap sediments and bedrock. In this paper, some of the major results obtained from deep resistivity sounding (DRS) studies in Saurashtra, Kutch and Deccan Syneclise regions are discussed Introduction The Detection and mapping of the sediments in the Deccan trap covered area has been a long-standing complex geophysical problem faced by the oil industry. In this direction, some of the geophysical methods like gravity, magnetic, electrical, seismic etc play an important and indispensable role in comprehending the various intricacies of the subsurface of the earth. Despite the fact that the geophysical industry witnessed an amazing all round development, spatial location of subsurface targets and geological translation of geophysical measurements/interpretation still poses a formidable challenge to the practicing geophysicists and at times continues to be cumbersome particularly when the targets of interest concealed under massive resistive basalt. The sediments underlying the basaltic layers are of varying thickness and cause considerable uncertainty in the interpretation of geophysical data. In recent times, geophysical prospecting has moved towards the use of integration of electrical methods with other geophysical methods for regional and prospect evaluation prior to drilling. Electrical methods in general and resistivity in particular have proven cost effective for exploration in basalt-covered area. Recently, non-seismic geophysical methods got wide attention in hydrocarbon exploration, especially in mapping the trapped sedimentary basins beneath the basaltic flows, which limits the seismic studies to a greater extent. The integrated explorative approach taken by NGRI in the basaltic covered regions of India, namely, Kutch, Saurashtra and Central Indian Deccan Syneclise (figure 1), evidenced significant Mesozoic sediments beneath the basaltic layers, prospective of future hydrocarbon explorations. The simultaneous use of Deep Resistivity Sounding (DRS), Magnetotellurics, gravity and seismics provide better resolution in the layer parameter estimations. The electrical resistivity contrast between the basaltic layers (Traps) and sedimentary layers provide a better opportunity to delineate the subsurface layers in these sub-volcanic provinces.